The present invention generally relates to medical diagnostic imaging systems, and in particular to X-ray collimator sizing and alignment in an X-ray imaging system employing a solid state X-ray detector.
Conventional X-ray imaging has found wide use in the medical diagnostic imaging industry. X-ray imaging systems are commonly used to capture, as examples, thoracic, cervical, spinal, cranial, and abdominal images that often include the information necessary for a doctor to make an accurate diagnosis. When having a thoracic X-ray image taken, for example, a patient stands with his or her chest against an X-ray sensor as an X-ray technologist positions the X-ray sensor and an X-ray source at an appropriate height. The X-ray energy generated by the source and attenuated to various degrees by different parts of the body, passes through the body and is detected by the X-ray sensor. An associated control system (where the X-ray sensor is a solid state imager) scans the detected X-ray energy and prepares a corresponding diagnostic image on a display. If the X-ray sensor is conventional film, the film is subsequently developed and displayed using a backlight.
Regulatory requirements mandate that imaging systems limit the X-ray field generated by the X-ray tube to an area that the X-ray sensor can acquire. X-ray imaging systems therefore use a collimator between the X-ray tube and the patient to constrain the X-ray field. To this end, the collimator may be constructed using horizontal and vertical lead blades that form an opening accurately corresponding to the X-ray sensor or desired anatomical area. During system calibration one must insure that the collimator blades can not be positioned at a size or orientation that allows imaging outside of the X-ray sensor. Furthermore, it is also of great importance that the horizontal and vertical blades are centered within the area of the X-ray sensor. These safeguards are required to prevent undesirable or unnecessary exposure of the patient to X-ray energy, and to insure excellent image quality.
In the past, however, the X-ray sensor was an X-ray sensitive screen and film combination. During system calibration a field engineer manually estimated the collimator sizing and centering using a field light positioned within the collimator. The field engineer then verified the calibration by exposing and developing the film. If measurements taken on the developed film indicated inappropriate collimator positioning, then the field engineer had to repeat the calibration process, after using a mechanical linkage and a screwdriver to manually adjust the collimator blade sizing and alignment. In the past, it was not uncommon for a single attempt at collimator calibration to require 5 or 6 minutes or more, and, taking into account repetition to ensure correct collimator sizing and alignment, as much as 30 minutes or more to finish calibration for a single size of film. Because most X-ray imaging systems are flexible enough to use numerous sizes and orientations of film (e.g., 14.times.17 and 17.times.14, 11.times.14 and 14.times.11, 8.times.10 and 10.times.8, as well as 5.times.7 and 7.times.5 inches), the field engineer required a significant amount of time to perform a complete collimator calibration. In addition, every calibration resulted in wasted film that could have been used to capture a diagnostic image for a doctor, and the accuracy attainable through manual collimator sizing and alignment was limited by human error.
A need has long existed for a method and apparatus for X-ray collimator sizing and alignment that overcomes the disadvantages discussed above and others previously experienced.